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SCEC Workshop - October 2003 Practical considerations for the future from a structural engineering perspective. Craig D. Comartin. Outline. Background on performance-based engineering Financial formulation of PBE Implications for practice Some important needs. PEER framing equation.

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SCEC Workshop - October 2003

Practical considerations for the future from a structural engineering perspective

Craig D. Comartin


Outline
Outline

  • Background on performance-based engineering

  • Financial formulation of PBE

  • Implications for practice

  • Some important needs


Peer framing equation
PEER framing equation

Decision variable

annualized loss

performance objective

Damage measure

casualties

capital loss

downtime

Engineering demandparameter

displacement

drift

Intensity measure

hazard curve

level of shaking

Pacific Earthquake Engineering Research Center


Decision should this building be retrofitted
Decision: Should this building be retrofitted?

Yes, if it is unsafe for shaking with a 10% chance of being exceeded in 50 yrs.

No, if it is safe for shaking with a 10% chance of being exceeded in 50 yrs.


Elements and components
Elements and Components

Returns included in properties

of components A1 and A5

A2

A3

A1

A5

A4

Wall element A

Wall element B

Components

Global Structure

Wall Element A



Component behavior and properties
Component Behavior and Properties

Backbone

curve

Force

Actual hysteretic

behavior

Deformation

Backbone curve from actual hysteretic behavior


Component behavior and properties1
Component Behavior and Properties

Backbone

Idealized component

curve

behavior

C

B, C, D

B

C, D

B

E

D

A

A

E

A

E

Ductile

Semi-ductile

Brittle

(force contolled)

(deformation controlled)

Idealized component behavior from backbone curves




Global force deformation relationship pushover or capacity curve
Global force-deformation relationship(Pushover or Capacity Curve)

D

Force

Parameter,

V

V

TOTAL

Displacement

Parameter,

D


Global displacement and damage
Global Displacement and Damage

Immediate

Life

Collapse

occupancy

safety

prevention

Building Damage States

Global

Force

Parameter

Global

capacity

curve

Global

Displacement

Limits, d

c

Performance Levels


Performance levels
Performance levels

Severe structural damage

Collapse

Prevention

Incipient Collapse

Probable

Probable falling hazards

total loss

Possible restricted egress

Probable structural damage

Life Safety

No Collapse

Possible

No falling hazards

total loss

Adequate emergency egress

Damage

Slight structural damage

Life safety attainable

Control

2 to 3

Essential systems repairable

Moderate overall damage

weeks

Negligible structural damage

Immediate

Occupancy

Life safety maintained

24

Essential systems operational

hours

Minor overall damage

Performance Level

Damage State

Down Time


Spectral representation
Spectral representation

Elastic spectrum


Nonlinear static analysis
Nonlinear static analysis

Elastic spectrum


Performance point
Performance point

Intensity measure

Damage measure

Global

Force

Parameter,

V

Building Damage States

Performance

Point

Global

capacity

curve

Immediate

Life

Collapse

Global

occupancy

safety

prevention

Displacement

m

Inelastic spectrum methods (R,

, T)

Limits, d

3.0

c

Performance Levels

m=1

m=2

2.0

m=4

m=8

Strength Demand (g)

1.0

Engineering demand parameter

0.0

0.0

1.0

2.0

3.0

4.0

Period,T (sec.)


Decision should this building be retrofitted1
Decision: Should this building be retrofitted?

No, if it is safe for shaking with a 10% chance of being exceeded in 50 yrs.


Decision should the structural system for this new building be upgraded
Decision: Should the structural system for this new building be upgraded?

Yes, if the benefits of the upgrade exceed the additional costs.


Force building be upgraded?

Sa

P(IM)

10-3

10-2

10-1

EDP

(displacement)

P(EDP)

T

Range of seismic intensity (IM)

Pushover curve

1.0

10-1

10-2

EDP

10-3

10-4

EDP (displacement) hazard

Engineering demand parameter and intensity measure


EDP to damage and loss building be upgraded?

Damage

Force

EDP

(displacement)

Loss

Casualties

Capital loss

Business interruption

EDP

(displacement)

Loss as a function of EDP

Pushover curve


P(Loss) building be upgraded?

Integrate for expected annual loss

1.0

10-1

P(EDP)

10-2

Loss

($)

10-3

10-4

Loss

Risk of Loss

1.0

10-1

EDP

(displacement)

10-2

EDP

10-3

10-4

EDP (displacement) hazard

Risk and expected annual loss

Loss as a function of EDP


UC Berkeley – Stanley Hall building be upgraded?

Item

Cost

Capital

$160 million

Contents

$50 million

Business Interruption

$40 million annually


Uc berkeley stanley hall
UC Berkeley – Stanley Hall building be upgraded?

$139K reduction in expected annual losses for unbonded braces compared to conventional system

Capital/Contents

Business Interruption

$400

$207

$300

($,000)

$200

$113

$100

$188

$143

$0

SCBF

(conventional braces)

UBB

(unbonded braces)


UC Berkeley – Stanley Hall building be upgraded?

$0.1

$0.6

$1.1

$1.7

$2.1

$2.4

$2.5

Benefit

$1.2

$1.2

$1.2

$1.2

$1.2

$1.2

$1.2

Cost

Benefit–cost ratio

(BCR)

2.5

2

5%

discount

1.5

1

0.5

0

1

5

10

20

30

40

50

Building Life (years)


Atc 58 performance based seismic design guidelines
ATC 58 Performance-based Seismic Design Guidelines building be upgraded?

Joe’s

Joe’s

Joe’s

Joe’s

Joe’s

Joe’s

Joe’s

Joe’s

Joe’s

Joe’s

Joe’s

Joe’s

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Food!

Operational

Operational

Immediate

Life

Life

Collapse

Collapse

Occupancy

Safety

Safety

Prevention

Prevention

Federal Emergency Management Agency

FEMA

-

349

  • Multiple Volumes

    • Seismic Performance Prediction for Buildings

    • Performance-based Seismic Design

    • Recommended Prescriptive Criteria for Performance-based Seismic Designs

Guidelines forPerformance-basedSeismic Design

Joe’s

Joe’s

Joe’s

Joe’s

Beer!

Beer!

Beer!

Beer!

Beer!

Beer!

Food!

Food!

Food!

Food!

Food!

Food!


Traditional traditional questions for structural engineer
Traditional traditional questions for structural engineer building be upgraded?

1. What is your fee?

2. Does it meet “code”?


Future questions for structural engineers
Future questions for structural engineers building be upgraded?

  • What would be the losses at my facility?

  • What is the return on investment in retrofit?

  • Does it pay to upgrade criteria for new construction?

  • What is a fair premium for insurance?

  • How does my seismic risk compare with others I face?


Fema 440 improvement of inelastic seismic analysis procedures
FEMA 440: Improvement of inelastic seismic analysis procedures

Equivalent Linearization

Displacement Modification

FEMA-356

Displacement Coefficient Method (DCM)

ATC- 40

Capacity Spectrum Method (CSM)


Nonlinear response history evaluation database
Nonlinear response history evaluation database procedures

20 NEHRP-B

20 NEHRP-C

SDOF oscillators

Ground motion records

Maximum displacements

(elastic plus inelastic)

20 NEHRP-D

20 NEHRP-E/F

20 NEAR-FAULT

50 periods of vibration (0.05s – 3.0s)

Damping ratio x=5%

180,000 total

9 levels of relative strength

R = 1 (elastic),1.5, 2, 3, 4, 5, 6, 7, 8

4 hysteretic behaviors (EPP, SD, SSD, NL)





Nonlinear static analysis1
Nonlinear static analysis procedures

Elastic spectrum



Multi degree of freedom mdof effects
Multi-degree-of-freedom (MDOF) effects procedures

Estimate response parameters made using simplified inelastic procedures.

Compare with results obtained by nonlinear dynamic analysis

from Aschheim 2002


Overturning moments weak story 9 story frame
Overturning Moments— Weak-story 9-story frame procedures

200000

200000

2% Drift

4% Drift

Overturning Moment (kips-ft)

Overturning Moment (kips-ft)

150000

150000

100000

100000

50000

50000

0

0

Floor

Floor

1st

1st

9th

8th

7th

6th

5th

4th

9th

8th

7th

6th

5th

4th

3rd

3rd

2nd

2nd

Weak—2 %

Weak—4 %

from Aschheim 2002


Potential simplified ndp
Potential simplified NDP procedures

200000

4% Drift

Overturning Moment (kips-ft)

150000

100000

50000

0

Floor

9th

8th

7th

6th

5th

4th

1st

3rd

2nd

  • Do NSP analysis to estimate global displacement.

  • Select one (few?) response histories and scale to result in same global displacement.

  • Use results to evaluate MDOF effects.


Factors that may reduce response of short period buildings
Factors that may reduce response of short period buildings procedures

1. Neglecting ascending branch of design spectra

2. Short, stiff buildings more sensitive to SSI

3. Radiation and material damping in supporting soils

4. Full and partial basements

5. Incoherent input to relatively large plan dimensions

6. Concentrating building masses at floor and roof levels


structural components of foundation procedures

geotechnical components of foundation

Infinitely rigid foundation and soil

ug= free field motion (FFM) with conventional damping

ug= free field motion (FFM) with conventional damping

a) Rigid base model

b) Flexible base model

ug= foundation input motion (FIM) with conventional damping

ug= foundation input motion (FIM) with system damping including foundation damping

Kinematic interaction

(high T-pass filter)

Adjust for foundation damping

Kinematic interaction

(high T-pass filter)

free field motion (FFM) with conventional damping

foundation input motion (FIM) with conventional damping

free field motion (FFM) with conventional damping

c) Kinematic interaction

d) Foundation damping


Example building for SSI effects procedures

160’-0”

100’-0”

8” R/C wall – 20’L

typical

Plan

20’-0”

Roof

10’-0”

typical

2nd

1st

3’D

Footing 26’L x 3’B x 1.5’t

Elevation @ wall

Section @ wall


Ssi example
SSI example procedures


Example building displacement modification procedure
Example building procedures(displacement modification procedure)

C

C

Procedure

Cap

Base

SSI

dy

T

Sa

R

d

mu

0

1

Current

yes

fixed

0.1

0.14

1.5

3.8

1.2

1.5

0.5

5.0

yes

flexible

0.2

0.21

1.5

3.8

1.2

1.4

1.1

5.4

no

fixed

0.1

0.14

1.5

3.8

1.2

3.4

1.2

11.8

no

flexible

0.2

0.21

1.5

3.8

1.2

2.4

1.8

9.2

Improved

fixed

no

0.1

0.14

1.5

3.8

1.2

2.6

0.9

8.8

fixed

yes

0.1

0.14

0.8

2.0

1.2

1.6

0.3

2.9

flexible

no

0.2

0.21

1.5

3.8

1.2

1.7

1.3

6.6

flexible

yes

0.2

0.21

0.8

2.0

1.2

1.3

0.5

2.6


Effects of foundations on performance
Effects of Foundations on Performance procedures

Foundation stiffness and strength affect

D

,large

Large

various structural components differently.

displacements

cause frame

High forces

damage

D

cause shear

, small

wall damage

Stiff and strong is not always favorable;

nor is flexible and weak always conservative.

Foundationyielding androcking protectsshear wall

Smalldisplacements

protect framefrom damage

Stiff and Strong Foundation

Flexible and Weak Foundation


Pier load tests
Pier load tests procedures

Dynamic

Static

Conventional estimates based on unconfined compression strength


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